[X] "Heal him." You may regret it, to be honest, but anyone brazen enough to assassinate a high lord in the middle of a tourney has some greater intrigue at work than pure opportunism. Better to suffer the consequences of being too free with magic on those who might resent the help than allow your enemies to succeed.
[X] Let him die, offer Doran to resurrect him later
-[X] Hunt down the assassin and get to the bottom of this
-[X] Make a note to give minor titles to Lord Fowler's daughters as a show of our appreciation for his loyalty, there are plenty of small plots of land they could rule in Essos